Communication System

ABSTRACT

A communications system is described that has a base station and a number of user devices, including legacy user devices and non-legacy user devices. The base station generates control data for transmission to the user devices, the control data including common control data for reception and decoding by a plurality of user devices and user specific control data for reception and decoding by a specific user device. The common control data is for reception and decoding by the non-legacy user devices and cannot be decoded by the legacy user devices. The common control data is repeated within multiple subframes for reception and decoding by non-legacy user devices. The non-legacy user devices are typically Machine Type Communications (MTC) user devices.

TECHNICAL FIELD

The present invention relates to mobile communications devices andnetworks, particularly but not exclusively those operating according tothe 3^(rd) Generation Partnership Project (3GPP) standards orequivalents or derivatives thereof. The invention has particularalthough not exclusive relevance to the Long Term Evolution (LTE) ofUTRAN (called Evolved Universal Terrestrial Radio Access Network(E-UTRAN)), including LTE-Advanced.

BACKGROUND ART

In a mobile (cellular) communications network, user devices (also knownas User Equipment (UE), for example mobile telephones) communicate withremote servers or with other user devices via base stations. In theircommunication with each other, user devices and base stations uselicensed radio frequencies, which are typically divided into frequencybands and/or time blocks.

In order to be able to communicate via the base stations, user devicesneed to monitor control channels operated by the base stations. One ofthese control channels, the so-called Physical Downlink Control Channel(PDCCH) carries the scheduling assignments and other controlinformation. The PDCCH serves a variety of purposes. Primarily, it isused to convey the scheduling decisions to individual user devices, i.e.scheduling assignments for uplink and downlink communication.

The information carried on the PDCCH is referred to as downlink controlinformation (DCI). Physical control channels, such as the PDCCH, aretransmitted on an aggregation of one or several consecutive ControlChannel Elements (CCEs), where a control channel element corresponds tonine Resource Element Groups (REGs). Each REG has four Resource Elements(REs).

Recent developments in telecommunications have seen a large increase inthe use of machine-type communications (MTC) user devices which arenetworked devices arranged to communicate and perform actions withouthuman assistance. Examples of such devices include smart meters, whichcan be configured to perform measurements and relay these measurementsto other devices via a telecommunication network. Machine-typecommunications are also known as machine 2 machine (M2M) communications.It is envisaged that MTC user devices will play an important role in theimplementation of the concept of the “internet of things”. It is commonfor MTC devices, such as smart meters or domestic appliances, to remainin a fixed location or exhibit low mobility. Such devices may also bedeployed deep inside buildings where network coverage is low. Forexample, some MTC user devices may be installed in the basement of aresidential building or in a location shielded by foil-backed insulationor metallised windows. These MTC devices will experience greaterpenetration losses on the air interface than normal user devices.

The lack of network coverage, in combination with the often limitedfunctionality of MTC user devices, can result in such MTC user deviceshaving a low data rate and therefore there is a risk of some messages orchannels, such as the PDCCH, not being received by an MTC user device.In order to mitigate this risk, it is desirable to increase the coverageof the PDCCH (and/or, where applicable, the evolved physical downlinkcontrol channel, EPDCCH).

One approach proposed for the enhancement of coverage is the repetitionof (E)PDCCH across multiple subframes. However, enhancing coveragepresents challenges relating to how carrier frequencies should beaggregated, how and where to signal a control channel in radio frames,and how to ensure that user equipment, including MTC and legacy devices,can efficiently locate and interpret the control signalling.

SUMMARY OF INVENTION

The present invention seeks to provide systems, devices and methodswhich at least partially address the above issues.

The present invention provides a communications node (such as a basestation) that schedules resources for use by a plurality of userdevices, including legacy user devices and non-legacy user devices, forcommunicating with the communications node, the communications nodecomprising: means for generating control data for transmission to theuser devices, the control data including common control data forreception and decoding by a plurality of user devices and user specificcontrol data for reception and decoding by a specific user device; andmeans for transmitting the generated control data in a sequence ofsubframes for reception by the user devices; wherein the means forgenerating is configured to generate common control data for receptionand decoding by the non-legacy user devices which cannot be decoded bythe legacy user devices; and wherein the means for transmitting isconfigured to transmit repeats of the common control data generated forreception and decoding by non-legacy user devices within a plurality ofsubframes.

In one exemplary embodiment, the control data is transmitted using aplurality of control channel elements, CCEs, and the common control datafor reception and decoding by the non-legacy user devices is transmittedusing an aggregation of at least sixteen CCEs that cannot be decoded bythe legacy user devices.

In another exemplary embodiment, the common control data for receptionand decoding by the non-legacy user devices is encrypted using anencryption key that is unavailable to the legacy user devices.

In another exemplary embodiment, the control data is transmitted in aphysical downlink common control channel, PDCCH, wherein common controldata for legacy user devices is located in a first part of the PDCCH anduser specific control data for legacy user devices is located in asecond part of the PDCCH; and wherein the common control data for thenon-legacy user devices is located in the second part of the PDCCH.

In another exemplary embodiment, each subframe includes a physicaldownlink common control channel, PDCCH, part and a physical downlinkshared channel, PDSCH, part and wherein the common control data forreception and decoding by the non-legacy user devices is transmittedwithin the PDSCH part of the subframe.

The communications node may be configured to transmit signallinginformation to the non-legacy user devices identifying the subframes inwhich the common control data for reception and decoding by thenon-legacy user devices is transmitted. In this case, the dataidentifying the subframes may identify only multimedia broadcast singlefrequency network, MBSFN, subframes as carrying the common control datafor reception and decoding by the non-legacy user devices.Alternatively, the data identifying the subframes may identifymultimedia broadcast single frequency network, MBSFN, subframes andnon-MBSFN subframes as carrying the common control data for receptionand decoding by the non-legacy user devices. In this case, thecommunications node may avoid placing the common control data forreception and decoding by the non-legacy user devices and channel stateinformation reference signals, CSI-RS, in the same subframe.

Typically, the communications node is configured to transmit saidsignalling information using a physical broadcast channel, PBCH. Wherethe communications node communicates with the user devices using radioframes having N subframes, the signalling information may comprise Nbits, one bit for identifying if a corresponding one of the N subframescarries the common control data for reception and decoding by thenon-legacy user devices. Alternatively, the signalling information maycomprise M bits, where M is less than N, that identify one of a numberof predetermined configuration of the N subframes that will carry thecommon control data for reception and decoding by the non-legacy userdevices. Where the data identifying the subframes identifies multimediabroadcast single frequency network, MBSFN, subframes and non-MBSFNsubframes as carrying the common control data for reception and decodingby the non-legacy user devices, the M bits may jointly or separatelyencode which MBSFN subframes and which non-MBSFN subframes of a radioframe will carry the common control data for reception and decoding bythe non-legacy user devices.

In some exemplary embodiments, the communications node is configured totransmit the common control data for reception and decoding by thenon-legacy user devices in subframes that do not include channel stateinformation reference signals, CSI-RS, or channel reference signals,CRS—or that do not include both CSI-RS and CRS reference signals.Alternatively, the communications node may transmit the common controldata for reception and decoding by the non-legacy user devices insubframes that include channel state information reference signals,CSI-RS, or channel reference signals, CRS; and avoids using resources tocarry the common control data for reception and decoding by thenon-legacy user devices that are used (or might be used) to carry theCSI-RS or the CRS.

In some exemplary embodiments, the communications node transmitssignalling information to the non-legacy user devices identifying thelocation within a subframe of the common control data for reception anddecoding by the non-legacy user devices. There may be a fixed number ofpossible locations within a subframe where the common control data maybe located, and in this case the communications node signals dataidentifying one of the possible locations. Alternatively, there may be afixed number of possible locations within a subframe for the commoncontrol data for reception and decoding by the non-legacy user devices,and the communications node may transmit the common control data in alocation that depends upon a static or semi static system variable, suchas a cell ID associated with the communications node.

In some exemplary embodiments, the communications node signals dataidentifying a size of the common control data for reception and decodingby the non-legacy user devices. In this case, the size of the commoncontrol data may be one of a plurality of possible sizes and thecommunications node may signal data indicating one of the plurality ofsizes to the non-legacy user devices.

Typically the common control data is carried on a plurality of resourceblocks, RBs, that may be either arranged contiguously within a subframeor dispersed within the subframe.

The present invention also provides a communications node that schedulesresources for use by a plurality of user devices for communicating withthe communications node, the communications node comprising: means forgenerating control data for transmission to the user devices, thecontrol data including common control data for reception and decoding bya plurality of user devices and user specific control data for receptionand decoding by a specific user device; means for generating referencesignals for use in controlling communications between the communicationsnode and the user devices; and means for transmitting the generatedreference signals and the generated control data in a sequence ofsubframes for reception by the user devices, each subframe including aphysical downlink common control channel, PDCCH, part and a physicaldownlink shared channel, PDSCH, part; wherein generated referencesignals and common control data for reception and decoding by aplurality of user devices are transmitted within the PDSCH part of thesubframe; and wherein the means for transmitting is configured totransmit said common control data and said reference signals within thePDSCH part of subframes using different resource blocks containedtherein.

The communications node may be configured to carry the common controldata in subframes that do not include channel state informationreference signals, CSI-RS, or channel reference signals, CRS.

The communications node may be configured to transmit the common controldata in subframes that include channel state information referencesignals, CSI-RS, or channel reference signals, CRS; and may beconfigured to avoid using resources to carry the common control datathat are used to carry the CSI-RS or the CRS.

In some exemplary embodiments, the communications node transmitssignalling information to the user devices identifying the locationand/or size, within a subframe, of the common control data.

Typically, the communications node starts said common control data on astarting symbol of the subframe that is known in advance by thenon-legacy user devices. The starting symbol may be different dependingon the type of subframe; and the non-legacy user device maintainsknowledge of the starting symbol to help identify the location of thecontrol data within the received subframe.

The present invention also provides a communications system comprisingthe above described communications node and at least one user device forreceiving and decoding the common control data to control communicationsbetween the user device and the communications node.

In one exemplary embodiment, the user device comprises: means forreceiving control data transmitted by the communications node, thecontrol data including common control data for reception and decoding bythe user device and user specific control data for reception anddecoding by a specific user device; wherein the received common controldata is for reception and decoding by non-legacy user devices and cannotbe decoded by legacy user devices; wherein the means for receiving isconfigured to receive a plurality of subframes comprising said commoncontrol data; means for combining the control data received from theplurality of subframes; and means for decoding the combined commoncontrol data.

In another exemplary embodiment, the user device comprises: means forreceiving subframes transmitted by the communications node, thesubframes comprising control data including common control data forreception and decoding by a plurality of user devices and user specificcontrol data for reception and decoding by a specific user device;wherein the subframes include reference signals transmitted by thecommunications node for use in controlling communications between thecommunications node and the user device; and wherein the means forreceiving is configured to receive a plurality of subframes comprisingsaid common control data; wherein each subframe includes a physicaldownlink common control channel, PDCCH, part and a physical downlinkshared channel, PDSCH, part; wherein received reference signals andcommon control data are received within the PDSCH part of the subframeusing different resource blocks contained within the PDSCH part; meansfor combining the control data received from the plurality of subframes;and means for decoding the combined common control data.

In another exemplary embodiment, the user device comprises: means forreceiving subframes transmitted by the communications node, thesubframes comprising control data including common control data forreception and decoding by a plurality of user devices and user specificcontrol data for reception and decoding by a specific user device;wherein the subframes include reference signals transmitted by thecommunications node for use in controlling communications between thecommunications node and the user device; and wherein the means forreceiving is configured to receive a plurality of subframes comprisingsaid common control data; wherein each subframe includes a physicaldownlink common control channel, PDCCH, part and a physical downlinkshared channel, PDSCH, part; wherein received reference signals andcommon control data are received within the PDSCH part of the subframeusing different resource blocks contained within the PDSCH part; meansfor identifying the common control data within the PDSCH part of thesubframes using information about the location, or the expectedlocation, of the reference control signals; means for combining thecontrol data received from the plurality of subframes; and means fordecoding the combined common control data.

Aspects of the invention extend to corresponding systems, methods, andcomputer program products such as computer readable storage media havinginstructions stored thereon which are operable to program a programmableprocessor to carry out a method as described in the aspects andpossibilities set out above or recited in the claims and/or to program asuitably adapted computer to provide the apparatus recited in any of theclaims.

Each feature disclosed in this specification (which term includes theclaims) and/or shown in the drawings may be incorporated in theinvention independently (or in combination with) any other disclosedand/or illustrated features. In particular but without limitation thefeatures of any of the claims dependent from a particular independentclaim may be introduced into that independent claim in any combinationor individually.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described by way of exampleonly with reference to the attached figures in which:

FIG. 1 schematically illustrates a telecommunication system;

FIG. 2 schematically illustrates a generic frame structure used incommunications over the wireless links of the system shown in FIG. 1;

FIG. 3 schematically illustrates the way in which the frequencysubcarriers are divided into resource blocks and the way that a timeslot is divided into a number of OFDM symbols;

FIG. 4 is a block diagram illustrating the main components of the userdevice shown in FIG. 1;

FIG. 5 is a block diagram illustrating the main components of the basestation shown in FIG. 1;

FIG. 6 illustrates a number of subframes forming part of a radio framefor the telecommunications system of FIG. 1;

FIG. 7 illustrates a modified PDCCH structure in which a block of CCEelements forming part of a USS portion of a legacy PDCCH is used forrepetitive signalling of control information for MTC devices;

FIG. 8 illustrates the way in which an EPDCCH can be repeated in anumber of subframes forming part of a radio frame for reception by anMTC device;

FIG. 9 illustrates one radio frame made up of 10 subframes andillustrating the possible locations of MBSFN subframes;

FIG. 10 shows a simplified illustration of a typical resource gridcorresponding to a subframe used in the telecommunication system of FIG.1;

FIG. 11 is a simplified illustration of exemplary resource gridscorresponding to a non-MBSFN subframe and an MBSFN subframe according toan option A;

FIG. 12 is a simplified illustration of exemplary resource gridscorresponding to a non-MBSFN subframe and an MBSFN subframe according toan option B;

FIG. 13 is a simplified illustration of an exemplary resource gridcorresponding to MBSFN subframes according to an option C;

FIG. 14 is a simplified illustration of exemplary resource gridscorresponding to a non-MBSFN subframe and an MBSFN subframe according toan option D; and

FIG. 15 is a view for use in describing another solution to design anenhanced CSS (ECCS) in EPDCCH for low cost MTC.

DESCRIPTION OF EMBODIMENTS Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 in which communication between user devices 3-0, 3-1 and 3-2 issupported by a base station 5 and a core network 7. In this exemplaryembodiment, user devices 3-0 and 3-1 are mobile telephones, and userdevice 3-2 is a machine-type communications (MTC) user device. As shown,user devices 3-0, 3-1 and 3-2 are located within a cell 6 operated bythe base station 5.

In the system illustrated in FIG. 1, the base station 5 shown is anEvolved Universal Terrestrial Radio Access Network (E-UTRAN) basestation. Such base stations are commonly referred to as eNBs (EvolvedNodeBs).

The base station 5 is configured to transmit an (E)PDCCH for receptionby the user devices 3 in the cell, the (E)PDCCH allocating uplink anddownlink resources to the user devices.

Also, base station 5 is configured to provide reference signals whichthe user devices 3 are operable to receive and use to determine signalquality. Based on the result of measurements, the user devices 3generate and send a report back to the base station 5. This feedbackmechanism is called channel quality indication (CQI) and, it is employedto fine-tune the operation of the base station 5, including resourceallocation, scheduling and power of transmission.

As will be described in more detail below, the base station 5 repeatsPDCCH transmissions for the MTC user device 3-2 and various alternativetechniques for doing so are described below. However, before describingthese alternatives, a brief overview of the LTE frame structure will nowbe given that will help to understand these alternative techniques.

LTE Subframe Data Structure

FIG. 2 schematically illustrates a generic frame structure used incommunications over the wireless links of the system shown in FIG. 1.

An orthogonal frequency division multiple access (OFDMA) technique isused for the downlink to allow the base station 5 to transmit user dataover the air interface to the respective user devices 3; and a singlecarrier frequency division multiple access (SC-FDMA) technique is usedfor the uplink to allow the user devices 3 to transmit their data overthe air interface to the base station 5. Different sub-carriers areallocated by the base station 5 (for a predetermined amount of time) toeach user device 3 depending on the amount of data to be sent in eachdirection. These sub-carriers and temporal allocations are defined asphysical resource blocks (PRBs) in the LTE specifications. PRBs thushave a time and frequency dimension. The base station 5 dynamicallyallocates PRBs for each device that it is serving and signals theallocations for each subframe (TTI) to each of the scheduled userdevices 3 in a control channel, e.g. (E)PDCCH.

As shown in FIG. 2, the generic frame structure agreed for LTEcommunications over the air interface includes a frame 13 which is 10msec long and which comprises ten subframes of 1 msec duration (known asa Transmission Time Interval (TTI)). Each subframe or TTI comprises twoslots 17 of 0.5 msec duration. Each slot 17 comprises either six orseven OFDMA symbols 19, depending on whether the normal or extendedcyclic prefix (CP) is employed.

FIG. 3 schematically illustrates the way in which the frequencysubcarriers are divided into resource blocks and the way that a timeslot is divided into a number of OFDM symbols.

The total number of available sub-carriers depends on the overalltransmission bandwidth of the system. The LTE specifications defineparameters for system bandwidths from 1.4 MHz to 20 MHz and one PRB iscurrently defined to comprise either 12 or 24 consecutive subcarriersfor one slot. A PRB over two slots is also defined by the LTEspecifications as being the smallest element of resource allocationassigned by the base station scheduler. These sub-carriers are thenmodulated onto a component carrier to up-convert the signal to thedesired transmission bandwidth.

The transmitted signal thus comprises N_(BW) subcarriers for a durationof N_(symb) symbols. Each box in the grid represents a singlesub-carrier for one symbol period and is referred to as a resourceelement. As shown in FIG. 3, in this case each PRB 11 is formed from 12consecutive sub-carriers and (in this example) seven symbols for eachsubcarrier; although in practice the same allocations are made in thesecond slot of each subframe as well. The control channel that includesthe resource allocation data for the user devices 3 is generallytransmitted in consecutive CCEs within the first three OFDM symbols ofeach subframe 15.

User device FIG. 4 is a block diagram illustrating the main componentsof the user device 3 shown in FIG. 1. The user device 3 may be an MTCuser device 3-2 or a mobile (or ‘cellular’) telephone capable ofoperating in a multi-carrier environment. The user device 3 comprises atransceiver circuit 401 which is operable to transmit signals to, and toreceive signals from, the base station 5 via at least one antenna 403.Typically, the user device 3 also includes a user interface 405 whichallows a user to interact with the user device 3, however this userinterface 405 may be omitted for some MTC user devices.

The operation of the transceiver circuit 401 is controlled by acontroller 407 in accordance with software stored in memory 409. Thesoftware includes, among other things, an operating system 411, acommunication control module 413, a measurement module 415, an (E)PDCCHconfiguration module 417 and an (E)PDCCH reception module 419.

The communication control module 413 is operable for managingcommunication with the base station 5. The measurement module 415receives measurement configuration information from the base station 5for the purposes of configuring the user device 3 to take measurementsof the CSI-RS (Channel State Information Reference Signal).

The measurement module 415 determines reference signal received power(RSRP) for the cells. In this exemplary embodiment, the measurementmodule 415 is operable to carry out signal quality measurements duringthe periods when the user device 3 is not scheduled to communicate withthe base station 5. Based on the result of measurements, the measurementmodule 415 generates and sends a CSI report (including the CQI) back tothe base station 5.

The (E)PDCCH configuration module 417 is operable to receive and process(E)PDCCH configuration information received from the base station 5,such as information identifying the location and size of the (E)PDCCHand/or an associated search space.

The (E)PDCCH reception module 419 is operable to search for, identifyand decode an (E)PDCCH, for example receiving DCI which signals aresource allocation for the user device.

Base Station

FIG. 5 is a block diagram illustrating the main components of the basestation 5 shown in FIG. 1. The base station 5 comprises an E-UTRANmulti-carrier capable base station comprising a transceiver circuit 501which is operable to transmit signals to, and to receive signals from,the user device 3 via one or more antennas 503. The base station 5 isalso operable to transmit signals to and to receive signals from a corenetwork 7 via a network interface 505. The operation of the transceivercircuit 501 is controlled by a controller 507 in accordance withsoftware stored in memory 509.

The software includes, among other things, an operating system 511, acommunication control module 513, a reference signal module 515, an(E)PDCCH configuration module 517 and an (E)PDCCH transmission module519.

The communication control module 513 is operable to controlcommunication with the user devices 3. The communication control module513 is also responsible for scheduling the resources to be used by theuser devices 3 served by this base station 5.

The reference signal module 515 is operable to transmit referencesignals for reception by the user devices 3, to allow the user devices 3to carry out signal quality measurements. The reference signal module515 controls which reference signals are transmitted and in whichresource elements and in which subframes.

The (E)PDCCH configuration module 517 is operable to generate andtransmit (E)PDCCH configuration information for the user devices 3, suchas information identifying the location and size of the (E)PDCCH and/oran associated search space.

The (E)PDCCH transmission module 519 is operable to transmit an(E)PDCCH, for example comprising DCI which signals a resource allocationfor a user device.

In the above description, the user device 3 and the base station 5 aredescribed for ease of understanding as having a number of discretemodules. Whilst these modules may be provided in this way for certainapplications, for example where an existing system has been modified toimplement the invention, in other applications, for example in systemsdesigned with the inventive features in mind from the outset, thesemodules may be built into the overall operating system or code and sothese modules may not be discernible as discrete entities.

Enhanced Coverage (E)PDCCH-(E)PDCCH Repetition

As discussed above, it is common for MTC user devices 3-2, such as smartmeters or domestic appliances, to remain in a fixed location or exhibitlow mobility; and to experience greater penetration losses on the airinterface than normal user devices. One approach proposed for theenhancement of coverage is the repetition of the (E)PDCCH for MTC userdevices 3-2 across multiple subframes.

FIG. 6 illustrates the way in which such repetition may be performedwithin five subframes 15. As shown in FIG. 6, the first part 142 of eachsubframe 15 is used to carry the PDCCH. The remainder of each subframe15 comprises the physical downlink shared channel (PDSCH) 143. The PDSCHresources for each user device 3 are allocated using control informationcarried in the PDCCH 142.

In this illustration, the PDCCH 142 of each subframe 15 includes controlinformation for both MTC user devices 3-2 and legacy user devices 3-0and 3-1. The PDCCH data for an MTC user device 3-2 is repeated insubframes 1 to 4. This PDCCH data informs the MTC user device 3-2 of anallocation of resources 147 within the PDSCH of subframe 5 for the MTCuser device 3-2. Thus the MTC user device 3-2 can combine the multiplePDCCH repetitions across subframes 1 to 4 before decoding the PDCCH todetermine its allocated resources 147 within the PDSCH.

In contrast, the PDCCH information for legacy user devices 3 is ingeneral not repeated across multiple subframes 15. The resourcesallocated to a particular legacy user device 3 within the PDSCH 145 of asubframe 15 are typically indicated in the PDCCH 142 of that subframe.As illustrated in FIG. 6, the particular resources allocated within thePDSCH may vary in each subframe.

Although not shown in FIG. 6, the PDCCH 142 consists of an aggregationof one or more consecutive control channel elements (CCEs), where a CCEoccupies a fraction of the base station's available physical resourceblocks (PBRs). In LTE, each CCE corresponds to nine resource elementgroups, where each resource element group corresponds to eight bits ofcontrolled data assuming QPSK modulation. The total number of CCEsavailable in a cell depends on the system bandwidth of the cell and thenumber of OFDM symbols reserved for PDCCH transmission in a givensubframe. As stated above, in this embodiment the first three OFDMsymbols of each subframe are dedicated to carrying the PDCCH controldata.

In order for an MTC user device 3-2 to be able to successfully receiveits (E)PDCCH, it is necessary for the MTC user device 3-2 to know thelocation of the CCEs in each subframe carrying the repetition of thePDCCH, along with the start subframe and end subframe for the repetitionand the timing of the subframe in which the resources 147 are allocatedrelative to the last of the subframes carrying the repeated PDCCH forthe MTC user device 3-2. In the example shown in FIG. 6, subframe 1 isthe start subframe, subframe 4 is the end subframe for the PDCCHrepetitions and the allocated resources 147 are located in subframe 5.

Those involved in the 3GPP standards have discussed how the (E)PDCCH andPDSCH will be configured for MTC user devices 3-2 where the enhancedcoverage of the (E)PDCCH is implemented using repetition. It has beenagreed that the relationship of PDSCH timing to (E)PDCCH timing shall beknown to user devices, for example, this timing may be fixed or the MTCuser devices 3-2 may be configured to derive it from other systeminformation. It has also been agreed that, from the perspective of anMTC user device 3-2, the possible starting subframes of the (E)PDCCHrepetitions are limited to a subset of subframes within a frame 13. Ithas also been agreed that where the (E)PDCCH is repeated across multiplesubframes, the resources 147 that are being allocated by the (E)PDCCHshall not be transmitted before the end of the (E)PDCCH repetitions.More specifically, if subframe n is the last (E)PDCCH repetition thenthe PDSCH starts at subframe n+k, where k>0.

It has also been agreed that the repetition of the (E)PDCCH can beconfigured for different signal to noise ratio (SNR) levels depending onthe channel quality indication (CQI) determined by a user device. Forexample, an MTC user device 3-2 located near the edge of the cell, the(E)PDCCH may be repeated 64 times, whereas an MTC user device locatedclose to the centre of the cell may receive only 16 repetitions. Varyingthe level of repetition of the (E)PDCCH helps to optimise powermanagement within the MTC user devices minimising unnecessaryrepetitions.

Search Spaces

User devices 3 do not know in advance when they will be signalled aresource allocation in the PDSCH, or which CCEs in the PDCCH will beused to signal those allocated resources. Therefore, each user device 3must scan the resources used for carrying the PDCCH for resourceallocation messages in every subframe 15. In order to keep thecomplexity of the process within reasonable limits, each user device 3searches only a subset of the CCEs in a subframe. This subset, includingall the possible locations of a PDCCH, is referred to as a search space.Each possible location of an (E)PDCCH is referred to as an ‘(E)PDCCHCandidate’.

As illustrated in FIG. 6, there are two types of search space: a commonsearch space (CSS) 151 and a UE-specific search space (USS) 153. A UE isrequired to monitor both common and UE-specific search spaces.

The common search space 151 carries downlink control information whichis common to all user devices 3. For example, the common search space151 may include system information blocks (SIBs) which containinformation related to cell access parameters, random access channel(RACH) message 2 (i.e. Random-Access Response) and RACH message 4 (i.e.Contention Resolution), and the paging channel (PCH). The maximum numberof CCEs present in the common search space is 16.

The UE-specific search space 153 carries downlink control informationfor particular user devices, such as UE-specific resource allocations.

Ideally, the size of a search space should be as small as possible tominimise the processing burden on the user devices 3. However, smallersearch spaces also place greater restrictions on the base station'sscheduling algorithm.

The number of CCEs making up one (E)PDCCH candidate is called theaggregation level, and the user device 3 search space contains (E)PDCCHswith a mixture of aggregation levels. Table 1 shows the typical size ofsearch spaces, which is based on the size of the legacy PDCCH searchspace.

TABLE 1 Search space S_(k) ^((L)) Type Aggregation level L Si

UE-specific 1

2

4

8

Common 4

8

indicates data missing or illegible when filed

While the agreements discussed above have been reached, there are stillnumerous problems to be solved in the implementation of enhancedcoverage of (E)PDCCH for MTC user devices 3-2.

For example, it is not clear which search space candidates should beused for (E)PDCCH and in turn which search space candidates should bemonitored by a user device. One possibility is that the location of theenhanced coverage (E)PDCCH could be based on the already defined searchspace candidates used for legacy PDCCH, as shown in Table 1. As shown,at aggregation level 8 there are only two candidates for the definedsearch space and therefore the MTC user device 3-2 would only need tocheck two possible locations for each DCI format. For any giventransmission, there could be downlink (DL) and/or uplink (UL) DCIformats. Therefore, in this case, the MTC user device 3-2 could assumethat for each repetition, the same first candidate is used for theDL-DCI format and the same second candidate is used for the UL-DCIformat, in order to facilitate coherent combining of data from therepetitions.

To date, the discussions surrounding the repetition of the (E)PDCCH haverelated to the repetition of the USS 153. There has been little or nodiscussion of the repetition of the CSS 151. However, the inventors haverealised that repeating the CSS 151 presents further problems. Inparticular, the USS 153 is configured so that it can only be decoded bythe user device 3 to which it relates and so repeating the USS 153 inseveral subframes does not cause problems for other user devices 3.However, since the CSS 151 is intended for receipt by all user devices3, there is a risk that legacy user devices 3 may mistakenly decode eachrepetition of the repeated (E)PDCCH as an allocation of the resources147 in the subframe carrying the repeated (E)PDCCH. The embodimentsdiscussed below aim to address or at least alleviate this problem.

Provision for Legacy User Devices in Enhanced Coverage PDCCH

It is important that the development of enhanced coverage PDCCH retainsbackwards compatibility with legacy user devices. The inventors proposeusing the legacy common search space (CSS) for the enhanced coveragePDCCH channel intended for the MTC user devices 3-2 and thereforerepetition of PDCCH control information will be implemented in thecommon search space as well as the UE-specific space (USS).

According to a first exemplary embodiment, confusion by legacy userdevices is avoided by employing an increased aggregation level for thePDCCH of MTC user devices 3-2. Specifically, an aggregation level of 16is employed, which means that the PDCCH takes up the entire CSS 151 (asthe maximum number of CCEs present in the common search space is 16).Legacy user devices 3 are only configured to be able to decode up to anaggregation level of 8 (see Table 1) and therefore the legacy userdevices 3 will not be able to decode a PDCCH at aggregation level 16 andthus the mistaken decoding of the repeated PDCCH by legacy user devices3 is avoided.

However, as the use of aggregation level 16 will result in the whole CSS151 of a subframe being consumed, there will not be any CCEs availablefor the base station 5 to schedule other control information. This mayresult in the blocking of the CSS 151 in a number of consecutivesubframes. Accordingly, the use of repeated PDCCH at aggregation level16 must be carefully considered to take into account these effects.

According to a second embodiment, the repeated PDCCH for MTC userdevices uses an aggregation level lower than that of 16, for exampleaggregation levels 4 or 8, and instead a specific scrambling is appliedto the PDCCH for MTC user devices 3-2. Preferably, this scrambling isapplied using a new Radio Network Temporary Identifier (RNTI).

Advantageously, scrambling prevents legacy devices 3 from mistakenlytrying to decode any of the PDCCH repetitions, and avoids all of theavailable CCEs of the CSS 151 being consumed as can occur in the firstembodiment (although there is still a possibility of blocking of the CSSin a number of consecutive subframes).

New Common Search Space in PDCCH for MTC User Devices

FIG. 7 illustrates a PDCCH according to a third embodiment. In thisembodiment, the PDCCH includes the legacy CSS 151 comprising 16 CCEs andthe USS 153 comprising N CCEs. However, as illustrated in FIG. 7, theUSS 153 comprises a new common search space for MTC user devices 3-2,labelled MTC-CSS 161. The new MTC-CSS 161 allows MTC user devices 3-2 toreceive the common control information, while avoiding legacy userdevices 3 attempting to decode this information, because the MTC-CSS 161is not provided in the legacy CSS search space 151.

In this example, the MTC-CSS 161 consists of 16 CCEs and startsimmediately after the legacy CSS 151. In this way the MTC user devices3-2 know where to look for the MTC-CSS—which reduces the search spacefor the MTC-CSS. Of course, the same advantage is achieved regardless ofwhere the MTC-CSS 161 is located within the USS, as long as its locationis known by the MTC user devices 3-2 in advance.

In this embodiment, the base station 5 prioritises the MTC-CSS 161 overthe UE-specific control information contained in the USS. Therefore,there is a degree of blocking of CCEs in the USS. However, as there aremore CCEs in the USS than in the CSS, the blocking probability for agiven user device is not severe.

Common Search Space in EPDCCH for MTC User Devices

As those skilled in the art will appreciate, the PDCCH is understood tobe contained within a set of symbols at the start of the subframe, forexample the first three symbols. As there is limited space within thePDCCH, it was proposed to transmit additional control data in the restof the subframe traditionally used for carrying the PDSCH. Thisadditional control data was defined to be contained within the “evolved”physical downlink control channel (EPDCCH). The way in which repetitionof the EPDCCH can be achieved will now be explained.

FIG. 8 illustrates a series of five subframes 15 forming part of a radioframe according to a fourth exemplary embodiment. In this exemplaryembodiment, a common search space for MTC user devices 3-2 is providedin the EPDCCH. In this example, each subframe 15 includes a PDCCH 142provided over the first three OFDM symbols. The remainder of eachsubframe comprises a PDSCH region 143 which can hold furthertransmissions such as the physical broadcast channel, PBCH, and theEPDCCH.

MTC user devices 3-2 often operate over a reduced bandwidth compared totypical user devices, and therefore in this exemplary embodiment theEPDCCH is provided within a reduced bandwidth of 1.4 MHz, whichcorresponds to 6 resource blocks.

In FIG. 8, the PDSCH region 143 of subframe 0 comprises a PBCHtransmission 173 which signals the location and size of an EPDCCH CSS171.

In order to signal the location of the EPDCCH CSS 171, multiple possiblelocations (N_(EPDCCH) _(_) _(location)) for the EPDCCH are predefined.The number of different locations is given by:

$N_{EPDCCH\_ location} = {N_{sb} = \left\lfloor \frac{N_{DL}^{RB}}{6} \right\rfloor}$

Where N_(DL) ^(RB) is the number of resource blocks across the wholedownlink system bandwidth.

Typically, the downlink system bandwidth may be 20 MHz, whichcorresponds to 100 resource blocks. Therefore, in this case there are 16different possible locations for the EPDCCH CSS.

One of the possible locations is signaled in the PBCH 173. Signallingthe location of the EPDCCH CSS 171 transmitted by the base station 5using the PBCH 173 beneficially allows the base station 5 to flexiblychoose the location.

Currently in PBCH 173, there are a total of 24 bits, in which 14 areused. Therefore, there are 10 spare bits in PBCH 173 which can be usedto signal the EPDCCH CSS 171. Methods for using these 10 bits to signalthis information to the MTC user device 3-2 are discussed further below.

In order to signal the size of the EPDCCH CSS 171, the base station(E)PDCCH transmission module 519 is configured by the (E)PDCCHconfiguration module 517 to use one of a number of possible sizes forthe EPDCCH CSS 171, in this exemplary embodiment either 2, 4 or 6 PRBswithin the reduced bandwidth of 1.4 MHz. Therefore, one of the possibleconfigurations is signaled by the base station 5 in the PBCH 173.Preferably, the 2, 4 or 6 PRBs are contiguous.

Common Search Space in EPDCCH for MTC User Devices—Accommodating RateMatching Parameters

When allocating the EPDCCH, the base station 5 must ensure there is noconflict with some of the reference signals that are transmitted withinsome subframes and the MTC user device 3-2 must know which resourceelements will form part of the EPDCCH and which resource elements carrythe reference signals. However, not all subframes of a radio frame willcarry all reference signals.

In LTE, providing broadcast data, in particular mobile television, is akey aspect. Broadcast services such as mobile television are provided bydedicated resources in the form of a multicast-broadcastsingle-frequency network (MBSFN). These MBSFN subframes do not carry allof these reference signals. It has been decided that a number ofparticular subframes within a radio frame are designated as potentialMBSFN subframes.

FIG. 9 illustrates one radio frame 13 made up of 10 subframes 15numbered 0 to 9. In common with previous Figures, the first part of eachsubframe comprises a PDCCH region 142 and the latter part of eachsubframe comprises a PDSCH region 143. In the example illustrated inFIG. 9, the radio frame 13 is a frequency division duplex (FDD) frameand accordingly subframes 1, 2, 3, 6, 7 and 8 are designated aspotential MBSFN subframes. It is noted that, for a time division duplex(TDD) frame, subframes 2, 3, 4, 7, 8 and 9 are designated as beingpotential MBSFN subframes.

In this example, the non-MBSFN subframes 0, 4, 5 and 9 include a PDCCHregion 142 which comprises three OFDM symbols, while MBSFN subframes 1,2, 3, 6, 7 and 8 include a reduced PDCCH region 142 which comprises onlytwo OFDM symbols.

Furthermore, the physical broadcast channel (PBCH) is provided inparticular subframes of a radio frame, in this example subframes 0 and 5are designated as possible PBCH subframes.

Reference Signals

FIG. 10 shows a simplified illustration of a typical resource grid of asubframe used in the telecommunication system 1 of FIG. 1. The subframecomprises a number of resource elements defined in time (i.e. in columnscorresponding to ‘symbols’ along the horizontal axis of FIG. 10) andfrequency (i.e. in rows corresponding to each ‘sub-carrier’ along thevertical axis of FIG. 10). Each EPDCCH consists of an aggregation ofcontrol channel elements (‘CCEs’). The PDCCH 142 is carried in the firstpart of the subframe 15, as shown generally in the left hand side areaof the subframe 15 of FIG. 10.

Some resource elements of the subframe are also used to carry cellreference signals (CRS) 154 and demodulation reference signals (DM RS)155, both of which are transmitted by the base station 5 periodically,at predetermined intervals and predetermined locations within asubframe. These signals are used to provide reference signal levels andto inform the user device 3 about the current operation of the basestation 5. Resource elements can be transmitted at varying energy levelsbut the CRS 154 resource elements are always transmitted at a known(e.g. a default) energy level. The user device 3 can thus carry outsignal quality measurements over the CRS 154 resource elements and,based on these measurements, can indicate to the base station 5 theperceived signal quality of a given frequency band (of a given cell)operated by the base station 5.

In addition to CRS and DM-RS, the base station 5 may also transmit achannel state information reference signal (CSI-RS). The CSI-RS is usedby user devices to determine the channel state and to report channelquality information (CQI) to the base station 5. CSI-RS is essentiallyan extension of the rate matching parameter CRS. In LTE Rel. 8, CRS wasdesigned for use in channel estimation for up to four layer spatialmultiplexing, where each antenna port (numbered ports 1 to 3) has aseparate CRS. However, extension of the reference signals was requiredwhen LTE Rel. 10 introduced further antenna nodes to support additionallayer spatial multiplexing (up to 8 layer spatial multiplexing). TheCSI-RS reference signal was added in preference to extending the CRS to8 layers as this would have added undesirable signalling overhead.CSI-RS is transmitted on different antenna ports (15 to 22) than CRS (0to 3), although the same physical antennas may be used. Furthermore,while CRS only uses time/frequency orthogonality, CSI-RS uses codedomain orthogonality in addition.

MBSFN subframes (such as subframes 1, 2, 3, 6, 7, 8 in FIG. 9) do notcarry cell specific reference signals such as CRS or CSI-RS becauseMBSFN subframes are not cell-specific.

As explained above, it is necessary for user devices to be aware ofwhich resource elements of the subframe contains the EPDCCH CSS 171.

In LTE Rel-11 a mapping parameter re-MappingQCL-ConfigId-r11 (asdescribed in 3GPP TS 36.213 section 9.1.4.3, the full disclosure ofwhich is hereby incorporated by reference) is used by user devices todetermine the mapping of the EPDCCH CSS to resource elements. Themapping parameter includes a CRS ports count parameter, denotedcrs-PortsCount-r11. This parameter is communicated to user devices onthe PBCH. The mapping parameter also includes a CRS frequency shiftparameter, crs-FreqShift-r11. This CRS frequency shift parameter isdetermined by a user device using the cell ID.

However, Rel-11 does not currently define how to inform a user device ofother important ratematching parameters, in particular the configurationof MBSFN subframes within the radio frame, the location of channel stateinformation reference signals (CSI-RS) in neighbouring cells, and thestarting OFDM symbol of the EPDDCH CSS. These three parameters arerespectively denoted as:

mbsfn-SubframeConfigList-r11;csi-RS-ConfigZPId-r11;pdsch-Start-r11.

A further ratematching parameter for the user devices 3 is the locationof the CSI-RS in the serving cell. This parameter is denotedqcl-CSI-RS-ConfigNZPId-r11. In this exemplary embodiment, the locationof the CSI-RS in the serving cell is configured in the same way as thelocation of CSI-RS in neighbouring cells, and therefore theqcl-CSI-RS-ConfigNZPId-r11 can be determined based oncsi-RS-ConfigZPId-r11.

In order for user devices to locate the EPDCCH CSS it is necessary forthe MTC user device 3-2 to obtain knowledge of the MBSFN subframeconfiguration, the CSI-RS configuration and the starting symbol of theEPDCCH CSS. Below are presented four options for providing theseparameters, described with reference to FIGS. 11 to 14.

Option A

FIG. 11 is a simplified illustration of exemplary resource grids 901 and903, resource grid 901 corresponding to a non-MBSFN subframe andresource grid 903 corresponding to an MBSFN subframe.

As shown, the non-MBSFN subframe 901 carries CRS type reference signals154 a and 154 b corresponding to antenna ports 0 to 3. The resourceelements used to carry CRS are distributed throughout the time andfrequency domain, where CRS for ports 0 and 1 are transmitted at symbols1, 5, 8 and 12. The CRS for ports 2 and 3 are transmitted at symbols 2and 9. The repetition of CRS resource elements corresponding to aparticular port across the frequency domain illustrates the fact thatCRS transmissions are frequency shifted for improved frequencydiversity.

As shown in FIG. 11, the MBSFN subframe 903 does not include any CRSsignals outside of the PDCCH because the CRS transmissions are cellspecific. However, the demodulation reference signals (DMRS) 155 arecarried by resource elements in both the non-MBSFN subframe 901 and theMSBSFN subframe 903. In this example, the DMRS resource elements arelocated at symbols 6, 7, 13 and 14 and are also frequency shifted.

According to option A, the PBCH channel is used to signal to the MTCuser device 3-2 which subframes out of the six possible MBSFN subframesof the radio frame are used for EPDCCH CSS 171. These MBSFN subframeswill not carry any CRS or CSI-RS transmissions outside of the PDCCH, andtherefore all of the unshaded resource elements in the MBSFN subframe903 can form part of the EPDCCH CSS 171.

Although all of these unshaded elements are available for EPDCCH CSS171, it is noted that in most embodiments a subset of the subcarrierswill be indicated by the PBCH 173 as carrying the EPDCCH CSS 171, andtherefore the EPDCCH CSS 171 may only occupy a subset of the carriersillustrated in FIG. 11.

Furthermore, if any other non-MBSFN subframes are signalled, in the PBCH173, to be used for EPDCCH CSS 171, then the MTC user device 3-2 assumesthat there are no CSI-RS transmissions present in the indicatednon-MBSFN subframes. Therefore, the EPDCCH CSS transmission can occupyall of the unshaded resource elements shown in the non-MBSFN subframe901. However, as these non-MBSFN subframes include DMRS or CRStransmissions, the corresponding resource elements are not available forthe EPDCCH CSS 171.

Accordingly, in option A the base station (E)PDCCH transmission module519 is configured by the (E)PDCCH configuration module 517 to avoidplacing the EPDCCH CSS 171 and CSI-RS in the same subframe.Alternatively, the base station (E)PDCCH transmission module 519 isconfigured by the (E)PDCCH configuration module 517 to puncture thecorresponding CSI-RS resource elements (RE) when mapping EPDCCH CSS 171to resource elements. In this case, if an EPDCCH CSS resource elementcollides with a CSI-RS location, then the CSI-RS is transmitted in thatlocation while the EPDCCH CSS resource element is not transmitted inthat location.

In option A, as shown in FIG. 11, the starting OFDM symbol for theEPDCCH CSS 171 is always fixed to the fourth OFDM symbol of the subframefor non-MBSFN subframes, as in these subframes the size of the PDCCH isthree symbols. In MBSFN subframes, the starting OFDM symbol for theEPDCCH CSS 171 is fixed to the third OFDM symbol of the subframe, as inthese subframes the size of the PDCCH is two symbols. In other exemplaryembodiments, the starting OFDM symbol could be another symbol (known inadvance) or the starting symbol could be signalled to the MTC userdevice 3-2 as well.

Option B

FIG. 12 is a simplified illustration of exemplary resource grids 1001and 1003, resource grid 1001 corresponding to a non-MBSFN subframe andresource grid 1003 corresponding to an MBSFN subframe.

As in option A, the non-MBSFN subframe 1001 carries CRS type referencesignals 154 a and 154 b corresponding to antenna ports 0 to 3, and theDMRS 155 are carried by resource elements in both the non-MBSFN subframe1001 and the MSBSFN subframe 1003. In this option, the PBCH channel isused to signal to the MTC user device 3-2 which subframes out of the sixpossible MBSFN subframes of the radio frame are used for the EPDCCH CSS171. The MBSFN subframes will not carry any CRS or CSI-RS transmissionsoutside of the PDCCH, and therefore all of the unshaded resourceelements in MBSFN subframe 1003 can form part of the EPDCCH CSS 171.

However, according to option B, the non-MBSFN subframe 1001 also carriesCSI-RS type reference signals 157 corresponding to antenna ports 0 to 7.All of the possible configurations of CSI-RS 157 are indicated insubframe 1001 of FIG. 12. Therefore, if non-MBSFN subframes aresignalled, in the PBCH 173, to be used for the EPDCCH CSS 171, then theMTC user device 3-2 assumes that all possible CSI-RS transmissions arepresent in the indicated non-MBSFN subframes. Therefore, the MTC userdevice 3-2 will exclude all of the potential CSI-RS REs from the EPDCCHCSS 171. The EPDCCH CSS 171 can occupy all of the unshaded resourceelements shown in the non-MBNSFN subframe 1001, which is a lower totalnumber of resource elements than in option A.

As in option A, although all of these unshaded elements are availablefor EPDCCH CSS 171, it is noted that in most exemplary embodiments asubset of the subcarriers will be indicated by the PBCH 173 as carryingthe EPDCCH CSS 171, and therefore the EPDCCH CSS 171 may only occupy asubset of the carriers illustrated in FIG. 12.

Thus, in accordance with option B, the base station 5 can place theEPDCCH CSS 171 and the CSI-RS in the same subframe.

In option B, like in option A and as shown in FIG. 12, the starting OFDMsymbol for the EPDCCH CSS 171 is fixed to the fourth OFDM symbol of thenon-MBSFN subframes while in MBSFN subframes the EPDCCH CSS 171 is fixedto the third OFDM symbol. Fixing the starting OFDM symbol reduces theamount of information that has to ne signalled to the MTC user device3-2.

Option C

FIG. 13 is a simplified illustration of an exemplary resource grid 1103corresponding to an MBSFN subframe.

As in options A and B, in option C the PBCH channel is used to signal tothe MTC user device 3-2 which subframes out of the six possible MBSFNsubframes of the radio frame are used for the EPDCCH CSS 171. The MBSFNsubframes 1103 will not carry any CRS or CSI-RS transmissions outside ofthe PDCCH, and therefore all of the unshaded resource elements in theMBSFN subframe 1103 can form part of the EPDCCH CSS 171. The DMRS 155 isalso carried by resource elements in the MSBSFN subframe 1103.

According to option C, the EPDCCH CSS 171 is not transmitted innon-MBSFN subframes. Therefore, there is no issue of how to transmit CRSand/or CSI-RS in the same subframe as the EPDCCH CSS 171.

As in options A and B, although all of the unshaded elements of subframe1103 are available for the EPDCCH CSS 171, it is noted that in mostembodiments a subset of the subcarriers will be indicated by the PBCH173 as carrying the EPDCCH CSS 171, and therefore the EPDCCH CSS 171 mayonly occupy a subset of the carriers illustrated in FIG. 13.

As in options A and B and as shown in FIG. 13, the starting OFDM symbolfor the EPDCCH CSS 171 is fixed to the third OFDM symbol of the MBSFNsubframe. As before, fixing the starting OFDM symbol reduces the amountof data that has to be signalled to the MTC user device 3-2.

Option D

FIG. 14 is a simplified illustration of exemplary resource grids 1201and 1203, resource grid 1201 corresponding to a non-MBSFN subframe andresource grid 1203 corresponding to an MBSFN subframe.

In option D, the PBCH channel is used to signal to the MTC user device3-2 which subframes are used for EPDCCH CSS 171, regardless of whetherthe subframes are MBSFN subframes or non-MBSFN subframes.

As in the previous options, the non-MBSFN subframe 1201 carries CRS typereference signals 154 a and 154 b corresponding to antenna ports 0 to 3,and the DMRS 155 are carried by resource elements in both the non-MBSFNsubframe 1201 and the MSBSFN subframe 1203.

As illustrated in FIG. 14, the non-MBSFN subframe 1201 does not carryCSI-RS transmissions, and therefore in option D the base station(E)PDCCH transmission module 519 is configured by the (E)PDCCHconfiguration module 517 to avoid placing the EPDCCH CSS 171 and theCSI-RS in the same subframe.

In option D, the MTC user device 3-2 does not distinguish betweennon-MBSFN and MBSFN subframes, and therefore the user device 3 assumesthat the same ratematching parameters are used in the non-MBSFN subframe1201 and the MBSFN subframe 1203. As a result, the user device willexclude “assumed CRS” resource elements 158 from the EPDCCH CSS 171 ofMBSFN subframes—even though those resource elements are not actuallybeing used to carry the CRS signals. Similarly, the user device willexclude “assumed PDCCH” resource elements 159 at the third OFDM symbolfrom the EPDCCH CSS 171 of MBSFN subframes, even though MBSFN subframesdo not include PDCCH at the third OFDM symbol.

Therefore, all of the unshaded resource elements in non-MBSFN subframe1201 and those in MBSFN subframe 1203 can form part of the EPDCCH CSS171.

As in the previous options, although all of these unshaded elements areavailable for EPDCCH CSS 171, it is noted that in most embodiments asubset of the subcarriers will be indicated by the PBCH 173 as carryingthe EPDCCH CSS 171, and therefore the EPDCCH CSS 171 may only occupy asubset of the carriers illustrated in FIG. 14.

In option D as shown in FIG. 14, the starting OFDM symbol for the EPDCCHCSS 171 is fixed to the fourth OFDM symbol of the subframe for bothnon-MBSFN and MBSFN subframes, as the user device 3 is configured toexclude the third symbol from the EPDCCH CSS 171 for MSBFN subframes.

Signalling of EPDCCH CSS Information

As discussed above, the physical broadcast channel PBCH 173 has only 10spare bits available for use in signaling information about the locationand size of the EPDCCH CSS 171 and in which subframes it is repeated.Three options for utilizing these 10 bits of the PBCH 173 are describedbelow.

Option 1

In this option, all 10 bits of the PBCH 173 are used by the base station5 to signal which subframes of a radio frame are used to carry therepeated EPDCCH CSS 171. Therefore, as there are 10 subframes in a radioframe, each bit corresponds to a single subframe. The subframes may beindicated as “on” or “off” with respect to the EPDCCH CSS 171, e.g. avalue of 0 means no EPDCCH CSS is present and a value of 1 means theEPDCCH CSS 171 is present. Accordingly, option 1 allows for everypossible configuration of subframes to be signaled.

However, this option consumes all available bits so there is no room forother signaling parameters such as the subband for the EPDCCH CSS(N_(EPDCCH) _(_) _(location)) and the number of PRB s configured forEPDCCH CSS 171. Therefore, if this option is used then the location andsize of the EPDCCH CSS 171 must be fixed in advance or must bedeterminable from some other information—such as from the cell ID orsignaled using other control information.

Option 2

In this option, the number of bits used to signal which subframes in aradio frame carry the EPDCCH CSS 171 is reduced, therefore reducing theflexibility in defining which subframes can be used. In this option,separate bits are coded for identifying which MBSFN subframes are usedto carry the EPDCCH CSS 171 and which non-MBSFN subframes are used tocarry the EPDCCH CSS 171. Table 2 below illustrates one example codingscheme that can be used in this option. As shown two bits are providedfor identifying which MBSFN subframes are used to carry the EPDCCH CSS171 and two bits are provided for identifying which non-MBSFN subframesare used to carry the EPDCCH CSS 171. Thus there are 8 differentsubframe configurations with this coding.

TABLE 2 6 MBSFN subframes for FDD 4 Non-MBSFN subframes for FDD 00 Notused. 00 No EPDCCH CSS configured in this cell. 01 1, 6 are used 01 0, 5are used 10 2, 3, 7, 8 are used 10 4, 9 are used 11 1, 2, 3, 6, 7, 8(all) are 11 0, 4, 5, 9 are used. used

The remaining six bits of the available ten bits in the PBCH 173 canthen be used to signal the location and size of the EPDCCH CSS 171within the band.

Option 3

This option also uses a reduced number of bits to signal which subframesare used to carry the EPDCCH CSS 171. However in option 3 joint codingof non-MBSFN and MBSFN subframes is used. Table 3 below illustrates oneexample joint coding scheme that can be used in this option. As shownthree bits are provided for identifying which subframes are used tocarry the EPDCCH CSS 171. As can be seen from Table 3, there are stilleight different subframe configurations with this joint coding schemewhich saves one bit compared to the coding scheme used in option 2discussed above.

TABLE 3 Joint coding of Non-MBSFN and MBSFN subframes for FDD 000 NoEPDCCH CSS configured in this cell 001 0, 5, 4, 9 are used 010 0, 5, 1,6 are used 011 0, 5, 2, 3, 7, 8 are used 100 0, 5, 1, 2, 3, 6, 7, 8 areused 101 4, 9, 2, 7 are used 110 4, 9, 1, 3, 6, 8 are used 111 4, 9, 1,2, 3, 6, 7, 8 are used

Thus the remaining seven bits of the available ten bits in the PBCH 173can be used to signal the location and size of the EPDCCH CSS 171 withinthe band.

Modifications and Alternatives

Detailed exemplary embodiments have been described above. As thoseskilled in the art will appreciate, a number of modifications andalternatives can be made to the above exemplary embodiments whilst stillbenefiting from the inventions embodied therein.

In the above description relating to the EPDCCH CSS 171, the EPDCCH CSS171 is provided within a reduced bandwidth of 1.4 MHz, and the locationof this reduced bandwidth is signalled by the PBCH 173. In analternative exemplary embodiment, the EPDCCH CSS 171 is not providedwithin a reduced bandwidth of 1.4 MHz. Instead, the PRBs reserved forthe EPDCCH CSS 171 are distributed over the system bandwidth (e.g. of 20MHz).

For example, the base station (E)PDCCH transmission module 519 may beconfigured by the (E)PDCCH configuration module 517 to use a fixednumber of PRBs for the EPDCCH CSS 171, in blocks of 2, 4 or 6 PRBs,which are distributed over the system bandwidth in a pre-configuredpattern. The MTC user device 3-2 will be pre-configured with the patternand then may determine the size of the blocks—2, 4, or 6 PRBs eitherfrom signaling information received from the base station 5 over thePBCH or by calculation using some cell specific information—such as thecell ID.

The base station 5 may define a number of possible locations where theEPDCCH CSS 171 can be located, with the locations being chosen inneighbouring cells to minimize inter cell interference. In this case,the selected location could also be signaled to the MTC user device overthe PBCH 173 or it could be determined from some (semi) staticinformation, such as from the cell ID.

In the above exemplary embodiments, a radio frame comprised 10subframes. As those skilled in the art will appreciate a radio frame mayinclude any number of subframes. Further, the PDCCH region of a subframemay comprise any number of OFDM symbols.

The legacy CSS 151 and the MTC-CSS 161 illustrated in FIG. 7 eachcomprise 16 CCEs, however as those skilled in the art will appreciate,both CSSs may comprise any number of CCEs.

Although the MTC-CSS 161 as illustrated in FIG. 7 commences immediatelyafter the legacy CSS, the MTC-CSS can be allocated anywhere in the USS.Preferably, the location within the USS is fixed.

In many of the exemplary embodiments described above, the EPDCCH isprovided within a reduced bandwidth of 1.4 MHz. This is not essential,other bandwidths are possible.

Similarly, in FIGS. 8 and 10 to 14, the EPDCCH CSS 171 startsimmediately after the PDCCH, specifically on the fourth OFDM symbol.However, the EPDCCH CSS 171 may be configured to start at any symbol.

In the description above, the location of the CSI-RS in the serving cellis configured in the same way as the location of CSI-RS in neighbouringcells, and therefore the qcl-CSI-RS-ConfigNZPId-r11 can be determinedbased on csi-RS-ConfigZPId-r11. Alternatively, the location of CSI-RSmay be configured differently in serving and neighbouring cells, andtherefore both qcl-CSI-RS-ConfigNZPId-r11 and csi-RS-ConfigZPId-r11 aresignalled to the user device 3 by the base station 5. In either case,when both parameters are configured, user devices are configured toassume no data (PDSCH/EPDCCH) is mapped on those locations (e.g. theEPDCCH CSS 171 does not include the resource elements carrying CSI-RS).

In the above description, information relating to the EPDCCH CSS 171,such as its location and size, is signaled in the PBCH 173.Alternatively or additionally, some or all of this information can beobtained by the user device in a different manner—for example thelocation and size may be signaled on a different channel.

Furthermore, the location of the EPDCCH CSS 171 may not be signaled inthe PBCH 173 and may instead be determined based upon other information,such as the Cell ID associated with the base station 5. Specifically,this may be determined in a cyclical manner, e.g by Cell ID modN_(EPDCCH) _(_) _(location). This has the benefit of reducing the amountof data that has to be signaled to the MTC user device, although in thiscase it is not practical to change the location based on prevailingradio conditions.

It will be appreciated that although the communication system 1 isdescribed in terms of base stations 5 operating as E-UTRAN basestations, the same principles may be applied to base stations operatingas macro or pico base stations, femto base stations, relay nodesproviding elements of base station functionality, home base stations(HeNB), or other such communication nodes.

In the above exemplary embodiments, an LTE telecommunications system wasdescribed. As those skilled in the art will appreciate, the signallingtechniques described in the present application can be employed in othercommunications systems, including earlier 3GPP type systems. Othercommunications nodes or devices may include user devices such as, forexample, personal digital assistants, laptop computers, web browsers,etc.

In the exemplary embodiments described above, the base stations 5 anduser devices 3 each include transceiver circuitry. Typically, thiscircuitry will be formed by dedicated hardware circuits. However, insome exemplary embodiments, part of the transceiver circuitry may beimplemented as software run by the corresponding controller.

In the above exemplary embodiments, a number of software modules weredescribed. As those skilled in the art will appreciate, the softwaremodules may be provided in compiled or un-compiled form and may besupplied to the base station or the user device as a signal over acomputer network, or on a recording medium. Further, the functionalityperformed by part or all of this software may be performed using one ormore dedicated hardware circuits.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

The following is a detailed description of the way in which the presentinventions may be implemented in the currently proposed 3GPP standard.Whilst various features are described as being essential or necessary,this may only be the case for the proposed 3GPP standard, for exampledue to other requirements imposed by the standard. These statementsshould not, therefore, be construed as limiting the present invention inany way.

INTRODUCTION

In RAN1#75, it has been agreed that repetition of (E-)PDCCH acrossmultiple sub-frames is supported for UEs in enhanced coverage mode oflow cost MTC. The agreements are as follows:

Agreements:

-   -   For UEs in enhanced coverage mode for MTC        -   For UE-specific search space,            -   (E)PDCCH to schedule PDSCH is supported.            -   Repetition of (E)PDCCH with multiple levels is                supported.            -   From the UE perspective, the possible starting                sub-frames of (E)PDCCH repetitions are limited to a                subset of sub-frames.    -   For UEs in enhanced coverage mode for MTC, if/when PDSCH is        indicated via (E)PDCCH:        -   The relation of PDSCH timing to (E)PDCCH timing shall be            known to UE and shall not be configurable by higher layer            parameter dedicated only for this purpose and shall not be            indicated by (E)PDCCH. FFS on how to derive it or fixed by            spec.        -   Assigned PDSCH is transmitted not before end of (E)PDCCH,            i.e., if subframe n is the last (E)PDCCH repetition then            PDSCH start n+k (k>0)

In this contribution, we discuss some details of the (E)PDCCH relatingUSS and CSS search space design for enhanced coverage of low cost MTCUEs and provide some proposals at the end.

UE Specific search space for MTC

In RAN1#75, repetition in time domain has been agreed for (E-)PDCCH forlow cost

MTC UEs in coverage enhanced mode. This means that UE has to combine(E-)PDCCH repetitions across multiple subframes in time domain. In orderUE to do that, UE has to know the location of CCEs from the search spacein each subframe as well as the start and end of subframes carrying therepetition of the (E-)PDCCH.

As discussed in the last meeting [5] and email discussion after themeeting, one possible way to determine the location of CCEs from the UEspecific search space (USS) is to use the same legacy PDCCH candidates“m” in Table 9.1.1-1 (TS 36.213 section 9.1) with same aggregation levelin each repetition, so that UE can combine each candidate with the samecandidate from the repeated subframes. For example aggregation level 8,there are two candidates based on existing Table 9.1.1-1, MTC UE cancombine each candidate from each repeated subframe, and when it reachesthe final repetition subframe, it tries to decode blindly thesecandidates similar to Release-8 (e.g. DL/UL DCI formats).

For E-PDCCH, the same principle as PDCCH can be applied. However, it isFFS whether to support higher aggregation levels than currentlysupported by E-PDCCH search space in order to reduce the number ofrepetitions in time-domain.

Furthermore, the timing of (E-)PDCCH to PDSCH has been agreed in thelast meeting which states that if subframe n is the last (E-)PDCCHrepetition then PDSCH start n+k (k>0). We think that the parameter “k”should be decided in such a way that the complexity of the schedulingdecisions are minimised, for example k=1.

Proposal 1: agree to determine the location of CCEs from the USS byusing the same legacy (E-)PDCCH candidates “m” with same aggregationlevel in each repetition, so that UE can combine them respectively.

Common search space for MTC

Common search space in PDCCH: common information such as SIB, RACHmessage 2/4 and PCH for MTC UEs can be sent on legacy common searchspace (CSS). However, as PDCCH for low cost MTC would be repeated inmultiple subframes before trying the actual decoding of the PDCCH, thelegacy UE may be confused or decode mistakenly the individual repeatedPDCCH in those subframes where there is no corresponding PDSCH carryingcommon control information. So, there are different possible solutionsas follows:

-   -   One way to avoid the legacy UE to decode repeated PDCCH is to        use aggregation level 16 (AL16) for low cost MTC. However, this        AL16 will consume the whole CSS space, meaning that there will        not be any remaining CCEs for eNB to schedule some other        important control information. Therefore, this solution causes        blocking of CSS in number of consecutive subframes. So, it is        not efficient solution.    -   Another way is to apply a specific scrambling on PDCCH that is        intended solely for low cost MTC. This kind of scrambling could        be a new RNTI (i.e. MTC-RNTI). However, based on this solution,        there is still concern that MTC UEs may consume a lot of        resources which may cause blocking of CSS in number of        consecutive subframes.

Common search space in EPDCCH: Another solution is to design an enhancedCSS (ECSS) in EPDCCH for low cost MTC as shown on FIG. 15. While thissolution solves the above issue, it also provides additional benefits ofapplying higher aggregation levels which will reduce the number ofrepetitions in time domain, power boosting, as well as interferencecoordination among cells. Some design principles for ECSS are:

-   -   The resources for ECSS in EPDCCH can be signaled in PBCH.    -   The ratematching parameters for ECSS can be determined as        follows:        -   Number of CRS ports, CRS-shift of non-MBSFN subframes used            for ECSS can be acquired from PBCH.        -   MBSFN subframes used for ECSS can be added in PBCH.        -   eNB can avoid placing ECSS on subframe(s) that contains            CSI-RS        -   Starting symbol for ECSS can be always fixed to 4^(th) and            3^(rd) OFDM symbol for non-MBSFN and MBSFN subframes            respectively.        -   Antenna port numbers and their initialization parameters            (e.g. c_(init) value) can be fixed and or derived from Cell            ID.

Proposal 2: consider a solution of how to avoid the legacy UE to decodemistakenly the individual repeated PDCCH in subframes where there is nocorresponding PDSCH carrying common control information.

Proposal 3: consider to introduce enhanced CSS (ECSS) in EPDCCH for lowcost MTC as it provides benefits of applying higher aggregation levelswhich will reduce the number of repetitions in time domain, powerboosting as well as interference coordination among cells.

CONCLUSION

In this contribution, we have discussed some details of the design of(E)PDCCH relating USS and CSS search spaces for enhanced coverage of lowcost MTC UEs and we have the following proposals:

Proposal 1: agree to determine the location of CCEs from the USS byusing the same legacy (E-)PDCCH candidates “m” with same aggregationlevel in each repetition, so that UE can combine them respectively.

Proposal 2: consider a solution of how to avoid the legacy UE to decodemistakenly the individual repeated PDCCH in subframes where there is nocorresponding PDSCH carrying common control information.

Proposal 3: consider to introduce enhanced CSS (ECSS) in EPDCCH for lowcost MTC as it provides benefits of applying higher aggregation levelswhich will reduce the number of repetitions in time domain, powerboosting as well as interference coordination among cells.

The whole or part of the exemplary embodiments disclosed above can bedescribed as, but not limited to, the following supplementary notes.

(Supplementary note 1). A communications node operable to scheduleresources for use by a plurality of user devices, including legacy userdevices and non-legacy user devices, for communicating with thecommunications node, the communications node comprising:

means for generating control data for transmission to the user devices,the control data including common control data for reception anddecoding by a plurality of user devices and user specific control datafor reception and decoding by a specific user device; and

means for transmitting the generated control data in a sequence ofsubframes for reception by the user devices;

wherein the means for generating is configured to generate commoncontrol data for reception and decoding by the non-legacy user deviceswhich cannot be decoded by the legacy user devices; and

wherein the means for transmitting is configured to transmit repeats ofthe common control data generated for reception and decoding bynon-legacy user devices within a plurality of subframes.

(Supplementary note 2). A communications node according to Supplementarynote 1, wherein the control data is transmitted using a plurality ofcontrol channel elements, CCEs, and wherein the common control data forreception and decoding by the non-legacy user devices is transmittedusing an aggregation of at least sixteen CCEs that cannot be decoded bythe legacy user devices.(Supplementary note 3). A communications node according to Supplementarynote 1, wherein the common control data for reception and decoding bythe non-legacy user devices is encrypted using an encryption key that isunavailable to the legacy user devices.(Supplementary note 4). A communications node according to Supplementarynote 1, wherein the control data is transmitted in a physical downlinkcommon control channel, PDCCH, wherein common control data for legacyuser devices is located in a first part of the PDCCH and user specificcontrol data for legacy user devices is located in a second part of thePDCCH; and wherein the common control data for the non-legacy userdevices is located in the second part of the PDCCH.(Supplementary note 5). A communications node according to Supplementarynote 1, wherein each subframe includes a physical downlink commoncontrol channel, PDCCH, part and a physical downlink shared channel,PDSCH, part and wherein the common control data for reception anddecoding by the non-legacy user devices is transmitted within the PDSCHpart of the subframe.(Supplementary note 6). A communications node according to Supplementarynote 5, wherein the communications node is configured to transmitsignalling information to the non-legacy user devices identifying thesubframes in which the common control data for reception and decoding bythe non-legacy user devices is transmitted.(Supplementary note 7). A communications node according to Supplementarynote 6, wherein the data identifying the subframes identifies onlymultimedia broadcast single frequency network, MBSFN, subframes ascarrying the common control data for reception and decoding by thenon-legacy user devices.(Supplementary note 8). A communications node according to Supplementarynote 6, wherein the data identifying the subframes identifies multimediabroadcast single frequency network, MBSFN, subframes and non-MBSFNsubframes as carrying the common control data for reception and decodingby the non-legacy user devices.(Supplementary note 9). A communications node according to Supplementarynote 8, wherein the communications node is configured to avoid placingthe common control data for reception and decoding by the non-legacyuser devices and channel state information reference signals, CSI-RS, inthe same subframe.(Supplementary note 10). A communications node according to any ofSupplementary notes 6 to 9, wherein the communications node isconfigured to transmit said signalling information using a physicalbroadcast channel, PBCH.(Supplementary note 11). A communications node according to any ofSupplementary notes 6 to 10, wherein the communications node isconfigured to communicate with the user devices using radio frameshaving N subframes and wherein the signalling information comprises Nbits, corresponding to one bit for identifying if a corresponding one ofthe N subframes carries the common control data for reception anddecoding by the non-legacy user devices.(Supplementary notes 12). A communications node according to any ofSupplementary notes 6 to 11, wherein the communications node isconfigured to communicate with the user devices using radio frameshaving N subframes and wherein the signalling information comprises Mbits, where M is less than N, that identify one of a number ofpredetermined configuration of the N subframes that will carry thecommon control data for reception and decoding by the non-legacy userdevices.(Supplementary note 13). A communications node according toSupplementary note 12, wherein the data identifying the subframesidentifies multimedia broadcast single frequency network, MBSFN,subframes and non-MBSFN subframes as carrying the common control datafor reception and decoding by the non-legacy user devices and whereinthe M bits jointly encode which MBSFN subframes and which non-MBSFNsubframes of a radio frame will carry the common control data forreception and decoding by the non-legacy user devices.(Supplementary note 14). A communications node according to any ofSupplementary notes 5 to 13, wherein the communications node isconfigured to transmit the common control data for reception anddecoding by the non-legacy user devices in subframes that do not includechannel state information reference signals, CSI-RS, or channelreference signals, CRS.(Supplementary note 15). A communications node according to any ofSupplementary notes 5 to 13, wherein the communications node isconfigured to transmit the common control data for reception anddecoding by the non-legacy user devices in subframes that includechannel state information reference signals, CSI-RS, or channelreference signals, CRS; and is configured to avoid using resources tocarry the common control data for reception and decoding by thenon-legacy user devices that are used to carry the CSI-RS or the CRS.(Supplementary note 16). A communications node according to any ofSupplementary notes 1 to 15, wherein the communications node isconfigured to transmit signalling information to the non-legacy userdevices identifying the location within a subframe of the common controldata for reception and decoding by the non-legacy user devices.(Supplementary note 17). A communications node according toSupplementary note 16, wherein there is a fixed number of possiblelocations within a subframe for the common control data for receptionand decoding by the non-legacy user devices, and wherein thecommunications node is configured to signal data identifying one of thepossible locations.(Supplementary note 18). A communications node according to any ofSupplementary notes 1 to 15, wherein there is a fixed number of possiblelocations within a subframe for the common control data for receptionand decoding by the non-legacy user devices, and wherein thecommunications node is configured to transmit the common control datafor reception and decoding by the non-legacy user devices in a locationthat depends upon a static or semi static system variable, such as acell ID associated with the communications node.(Supplementary note 19). A communications node according to any ofSupplementary notes 1 to 18, wherein the communications node isconfigured to signal data identifying a size of the common control datafor reception and decoding by the non-legacy user devices.(Supplementary note 20). A communications node according toSupplementary note 19, wherein the size of the common control data forreception and decoding by the non-legacy user devices is one of aplurality of possible sizes and wherein the communications node isconfigured to signal data indicating one of the plurality of sizes.(Supplementary note 21). A communications node according to any ofSupplementary notes 1 to 20, wherein the common control data forreception and decoding by the non-legacy user devices is carried on aplurality of resource blocks, RBs, and wherein the RBs are eitherarranged contiguously within a subframe or are dispersed within asubframe.(Supplementary note 22). A communications node operable to scheduleresources for use by a plurality of user devices for communicating withthe communications node, the communications node comprising:

means for generating control data for transmission to the user devices,the control data including common control data for reception anddecoding by a plurality of user devices and user specific control datafor reception and decoding by a specific user device;

means for generating reference signals for use in controllingcommunications between the communications node and the user devices; and

means for transmitting the generated reference signals and the generatedcontrol data in a sequence of subframes for reception by the userdevices, each subframe including a physical downlink common controlchannel, PDCCH, part and a physical downlink shared channel, PDSCH,part;

wherein generated reference signals and common control data forreception and decoding by a plurality of user devices are transmittedwithin the PDSCH part of the subframe; and

wherein the means for transmitting is configured to transmit said commoncontrol data and said reference signals within the PDSCH part ofsubframes using different resource blocks contained therein.

(Supplementary note 23). A communications node according toSupplementary note 22, wherein the communications node is configured tocarry the common control data in subframes that do not include channelstate information reference signals, CSI-RS, or channel referencesignals, CRS.(Supplementary note 24). A communications node according toSupplementary note 22 or 23, wherein the communications node isconfigured to transmit the common control data in subframes that includechannel state information reference signals, CSI-RS, or channelreference signals, CRS; and is configured to avoid using resources tocarry the common control data that are used to carry the CSI-RS or theCRS.(Supplementary note 25). A communications node according to any ofSupplementary notes 22 to 24, wherein the communications node isconfigured to transmit signalling information to the user devicesidentifying the location within a subframe of the common control data.(Supplementary note 26). A communications node according toSupplementary note 25, wherein there is a fixed number of possiblelocations within a subframe for the common control data and wherein thecommunications node is configured to signal data identifying one of thepossible locations.(Supplementary note 27). A communications node according toSupplementary note 25, wherein there is a fixed number of possiblelocations within a subframe for the common control data and wherein thecommunications node is configured to transmit the common control data ina location that depends upon a static or semi static system variable,such as a cell ID associated with the communications node.(Supplementary note 28). A communications node according to any ofSupplementary notes 22 to 27, wherein the communications node isconfigured to transmit signalling information to the non-legacy userdevices identifying the subframes in which the common control data istransmitted.(Supplementary note 29). A communications node according toSupplementary note 28, wherein the data identifying the subframesidentifies only multimedia broadcast single frequency network, MBSFN,subframes as carrying the common control data.(Supplementary note 30). A communications node according toSupplementary notes 28 or 29, wherein the data identifying the subframesidentifies multimedia broadcast single frequency network, MBSFN,subframes and non-MBSFN subframes as carrying the common control data.(Supplementary note 31). A communications node according toSupplementary note 30, wherein the communications node is configured toavoid placing the common control data for reception and decoding by thenon-legacy user devices and channel state information reference signals,CSI-RS, in the same subframe.(Supplementary note 32). A communications node according to any ofSupplementary notes 28 to 31, wherein the communications node isconfigured to transmit said signalling information using a physicalbroadcast channel, PBCH.(Supplementary note 33). A communications node according to any ofSupplementary notes 28 to 32, wherein the communications node isconfigured to communicate with the user devices using radio frameshaving N subframes and wherein the signalling information comprises Nbits, corresponding to one bit for identifying if a corresponding one ofthe N subframes carries the common control data.(Supplementary note 34). A communications node according to any ofSupplementary notes 28 to 33, wherein the communications node isconfigured to communicate with the user devices using radio frameshaving N subframes and wherein the signalling information comprises Mbits, where M is less than N, that identify one of a number ofpredetermined configuration of the N subframes that will carry thecommon control data.(Supplementary note 35). A communications node according toSupplementary note 34, wherein the data identifying the subframesidentifies multimedia broadcast single frequency network, MBSFN,subframes and non-MBSFN subframes as carrying the common control dataand wherein the M bits jointly encode which MBSFN subframes and whichnon-MBSFN subframes of a radio frame will carry the common control data.(Supplementary note 36). A communications node according to any ofSupplementary notes 1 to 35, wherein the non-legacy user devices includeMachine Type Communications, MTC, user devices.(Supplementary note 37). A communications node according to any ofSupplementary notes 1 to 36, wherein the communications node starts saidcommon control data on a starting symbol of the subframe that is knownin advance by the non-legacy user devices.(Supplementary note 38). A communications system comprising acommunications node according to any of Supplementary notes 1 to 37 andat least one user device for receiving and decoding the common controldata to control communications between the user device and thecommunications node.(Supplementary note 39). A user device for communicating with acommunications node, characterised in that the user device is configuredto operate with the communications node of any of Supplementary notes 1to 37 and adapted to be able to receive and decode the common controldata to control communications with the communications node.(Supplementary note 40). A method performed by a communications nodethat schedules resources for use by a plurality of user devices,including legacy user devices and non-legacy user devices, forcommunicating with the communications node, the method comprising:

generating control data for transmission to the user devices, thecontrol data including common control data for reception and decoding bya plurality of user devices and user specific control data for receptionand decoding by a specific user device; and

transmitting the generated control data in a sequence of subframes forreception by the user devices;

wherein the generating generates common control data for reception anddecoding by the non-legacy user devices which cannot be decoded by thelegacy user devices; and

wherein the transmitting transmits repeats of the common control datagenerated for reception and decoding by non-legacy user devices within aplurality of subframes.

(Supplementary note 41). A method performed by a communications nodethat schedules resources for use by a plurality of user devices forcommunicating with the communications node, the method comprising:

generating control data for transmission to the user devices, thecontrol data including common control data for reception and decoding bya plurality of user devices and user specific control data for receptionand decoding by a specific user device;

generating reference signals for use in controlling communicationsbetween the communications node and the user devices; and

transmitting the generated reference signals and the generated controldata in a sequence of subframes for reception by the user devices, eachsubframe including a physical downlink common control channel, PDCCH,part and a physical downlink shared channel, PDSCH, part;

wherein generated reference signals and common control data forreception and decoding by a plurality of user devices are transmittedwithin the PDSCH part of the subframe; and

wherein the transmitting is configured to transmit said common controldata and said reference signals within the PDSCH part of subframes usingdifferent resource blocks contained therein.

(Supplementary note 42). A communications node operable to scheduleresources for use by a plurality of user devices, including legacy userdevices and non-legacy user devices, for communicating with thecommunications node, the communications node comprising:

a control configuration module for generating control data fortransmission to the user devices, the control data including commoncontrol data for reception and decoding by a plurality of user devicesand user specific control data for reception and decoding by a specificuser device; and

a transmitter for transmitting the generated control data in a sequenceof subframes for reception by the user devices;

wherein the control configuration module is configured to generatecommon control data for reception and decoding by the non-legacy userdevices which cannot be decoded by the legacy user devices; and

wherein the transmitter is configured to transmit repeats of the commoncontrol data generated for reception and decoding by non-legacy userdevices within a plurality of subframes.

(Supplementary note 43). A communications node operable to scheduleresources for use by a plurality of user devices for communicating withthe communications node, the communications node comprising:

a control configuration module for generating control data fortransmission to the user devices, the control data including commoncontrol data for reception and decoding by a plurality of user devicesand user specific control data for reception and decoding by a specificuser device;

a reference signal module for generating reference signals for use incontrolling communications between the communications node and the userdevices; and

a transmitter for transmitting the generated reference signals and thegenerated control data in a sequence of subframes for reception by theuser devices, each subframe including a physical downlink common controlchannel, PDCCH, part and a physical downlink shared channel, PDSCH,part;

wherein generated reference signals and common control data forreception and decoding by a plurality of user devices are transmittedwithin the PDSCH part of the subframe; and

wherein the transmitter is configured to transmit said common controldata and said reference signals within the PDSCH part of subframes usingdifferent resource blocks contained within the PDSCH part.

(Supplementary note 44). A user device for communicating with acommunications node, the user device comprising:

means for receiving control data transmitted by the communications node,the control data including common control data for reception anddecoding by the user device and user specific control data for receptionand decoding by a specific user device;

wherein the received common control data is for reception and decodingby non-legacy user devices and cannot be decoded by legacy user devices;

wherein the means for receiving is configured to receive a plurality ofsubframes comprising said common control data;

means for combining the control data received from the plurality ofsubframes; and

means for decoding the combined common control data.

(Supplementary note 45). A user device for communicating with acommunications node, the user device comprising:

means for receiving subframes transmitted by the communications node,the subframes comprising control data including common control data forreception and decoding by a plurality of user devices and user specificcontrol data for reception and decoding by a specific user device;

wherein the subframes include reference signals transmitted by thecommunications node for use in controlling communications between thecommunications node and the user device; and

wherein the means for receiving is configured to receive a plurality ofsubframes comprising said common control data;

wherein each subframe includes a physical downlink common controlchannel, PDCCH, part and a physical downlink shared channel, PDSCH,part;

wherein received reference signals and common control data are receivedwithin the PDSCH part of the subframe using different resource blockscontained within the PDSCH part;

means for combining the control data received from the plurality ofsubframes; and

means for decoding the combined common control data.

(Supplementary note 46). A user device for communicating with acommunications node, the user device comprising:

a receiver for receiving control data transmitted by the communicationsnode, the control data including common control data for reception anddecoding by the user device and user specific control data for receptionand decoding by a specific user device;

wherein the received common control data is for reception and decodingby non-legacy type user devices and cannot be decoded by legacy typeuser devices;

wherein the receiver is configured to receive a plurality of subframescomprising said common control data; and

a control channel reception module for combining the control datareceived from the plurality of subframes and for decoding the combinedcommon control data.

(Supplementary note 47). A user device for communicating with acommunications node, the user device comprising:

a receiver for receiving subframes transmitted by the communicationsnode, the subframes comprising control data including common controldata for reception and decoding by a plurality of user devices and userspecific control data for reception and decoding by a specific userdevice;

wherein the subframes include reference signals transmitted by thecommunications node for use in controlling communications between thecommunications node and the user device; and

wherein the receiver is configured to receive a plurality of subframescomprising said common control data;

wherein each subframe includes a physical downlink common controlchannel, PDCCH, part and a physical downlink shared channel, PDSCH,part;

wherein received reference signals and common control data are receivedwithin the PDSCH part of the subframe using different resource blockscontained within the PDSCH part; and

a control channel reception module for combining the control datareceived from the plurality of subframes and for decoding the combinedcommon control data.

(Supplementary note 48). A method performed by a user device thatcommunicates with a communications node, the method comprising:

receiving control data transmitted by the communications node, thecontrol data including common control data for reception and decoding bythe user device and user specific control data for reception anddecoding by a specific user device;

wherein the received common control data is for reception and decodingby non-legacy user devices and cannot be decoded by legacy user devices;

wherein the receiving receives a plurality of subframes comprising saidcommon control data;

combining the control data received from the plurality of subframes; and

decoding the combined common control data.

(Supplementary note 49). A method performed by a user device thatcommunicates with a communications node, the method comprising:

receiving subframes transmitted by the communications node, thesubframes comprising control data including common control data forreception and decoding by a plurality of user devices and user specificcontrol data for reception and decoding by a specific user device;

wherein the subframes include reference signals transmitted by thecommunications node for use in controlling communications between thecommunications node and the user device; and

wherein the receiving receives a plurality of subframes comprising saidcommon control data;

wherein each subframe includes a physical downlink common controlchannel, PDCCH, part and a physical downlink shared channel, PDSCH,part;

wherein received reference signals and common control data are receivedwithin the PDSCH part of the subframe using different resource blockscontained within the PDSCH part;

combining the control data received from the plurality of subframes; and

decoding the combined common control data.

(Supplementary note 50). A communications node operable to scheduleresources for use by a plurality of user devices, including first typeuser devices and second type user devices, for communicating with thecommunications node, the communications node comprising:

means for generating control data for transmission to the user devices,the control data including common control data for reception anddecoding by a plurality of user devices and user specific control datafor reception and decoding by a specific user device; and

means for transmitting the generated control data in a sequence ofsubframes for reception by the user devices;

wherein the means for generating is configured to generate commoncontrol data for reception and decoding by second type user deviceswhich cannot be decoded by first type user devices; and

wherein the means for transmitting is configured to transmit repeats ofthe common control data generated for reception and decoding by secondtype user devices within a plurality of subframes.

(Supplementary note 51). A communications node according toSupplementary note 50, wherein the first type user devices are legacyuser devices and wherein the second type user devices are non-legacyuser devices.(Supplementary note 52). A communications node operable to scheduleresources for use by a plurality of user devices for communicating withthe communications node, the communications node comprising:

means for generating control data for transmission to the user devices,the control data including common control data for reception anddecoding by a plurality of user devices and user specific control datafor reception and decoding by a specific user device;

means for transmitting the generated control data in a sequence ofsubframes for reception by the user devices, each subframe including aphysical downlink common control channel, PDCCH, part and a physicaldownlink shared channel, PDSCH, part;

wherein the means for transmitting is configured to transmit repeats ofthe common control data generated for reception and decoding bynon-legacy user devices within a plurality of subframes; and

wherein the communications node is configured to transmit signallinginformation to the non-legacy user devices identifying the subframes inwhich the common control data for reception and decoding by thenon-legacy user devices is transmitted.

(Supplementary note 53). A user device for communicating with acommunications node, the user device comprising:

means for receiving subframes transmitted by the communications node,the subframes comprising control data including common control data forreception and decoding by a plurality of user devices and user specificcontrol data for reception and decoding by a specific user device;

wherein the subframes include reference signals transmitted by thecommunications node for use in controlling communications between thecommunications node and the user device; and

wherein the means for receiving is configured to receive a plurality ofsubframes comprising said common control data;

wherein each subframe includes a physical downlink common controlchannel, PDCCH, part and a physical downlink shared channel, PDSCH,part;

wherein received reference signals and common control data are receivedwithin the PDSCH part of the subframe using different resource blockscontained within the PDSCH part;

means for identifying the common control data within the PDSCH part ofthe subframes using information about the location, or the expectedlocation, of the reference control signals;

means for combining the control data received from the plurality ofsubframes; and

means for decoding the combined common control data.

(Supplementary note 54). A user device according to Supplementary note53, wherein the means for identifying is further configured to use datasignalled from the communications node to identify the common controldata within the PDSCH part of the subframes.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1401459.1, filed on Jan. 28, 2014,the disclosure of which is incorporated herein in its entirety byreference.

What is claimed is:
 1. A communications node operable to scheduleresources for use by a plurality of user devices, including legacy userdevices and Machine Type Communications, MTC user devices, forcommunicating with the communications node, the communications nodecomprising: a controller configured to generate control data fortransmission to the user devices, the control data including commoncontrol data for reception and decoding by a plurality of user devicesand user specific control data for reception and decoding by a specificuser device; and a transceiver circuit configured to transmit thegenerated control data in a sequence of subframes for reception by theuser devices; wherein the controller is further configured to generatecommon control data for reception and decoding by the MTC user devices;wherein the transceiver circuit is further configured to transmit thecommon control data for the legacy user devices on a first channel andthe common control data for the MTC user devices on a second channelwhich is not monitored by the legacy user devices; and wherein thetransceiver is further configured to transmit repeats of the commoncontrol data generated for reception and decoding by the MTC userdevices within a plurality of subframes.
 2. A communications nodeaccording to claim 1, wherein the control data is transmitted using aplurality of control channel elements, CCEs, and wherein the commoncontrol data for reception and decoding by the MTC user devices istransmitted using an aggregation of at least sixteen CCEs that cannot bedecoded by the legacy user devices.
 3. A communications node accordingto claim 1, wherein the common control data for reception and decodingby the MTC user devices is encrypted using an encryption key that isunavailable to the legacy user devices.
 4. A communications nodeaccording to claim 1, wherein the control data is transmitted in aphysical downlink common control channel, PDCCH, wherein common controldata for legacy user devices is located in a first part of the PDCCH anduser specific control data for legacy user devices is located in asecond part of the PDCCH; and wherein the common control data for theMTC user devices is located in the second part of the PDCCH.
 5. Acommunications node according to claim 1, wherein each subframe includesa physical downlink common control channel, PDCCH, part and a physicaldownlink shared channel, PDSCH, part and wherein the common control datafor reception and decoding by the MTC user devices is transmitted withinthe PDSCH part of the subframe.
 6. A communications node according toclaim 5, wherein the communications node is configured to transmitsignalling information to the MTC user devices identifying the subframesin which the common control data for reception and decoding by the MTCuser devices is transmitted.
 7. A communications node according to claim6, wherein the data identifying the subframes identifies only multimediabroadcast single frequency network, MBSFN, subframes as carrying thecommon control data for reception and decoding by the MTC user devices.8. A communications node according to claim 6, wherein the dataidentifying the subframes identifies multimedia broadcast singlefrequency network, MBSFN, subframes and non-MBSFN subframes as carryingthe common control data for reception and decoding by the MTC userdevices.
 9. A communications node according to claim 8, wherein thecommunications node is configured to avoid placing the common controldata for reception and decoding by the MTC user devices and channelstate information reference signals, CSI-RS, in the same subframe.
 10. Acommunications node according to claim 6, wherein the communicationsnode is configured to transmit said signalling information using atleast one system information block, SIB.
 11. A communications nodeaccording to claim 6, wherein the communications node is configured tocommunicate with the user devices using radio frames having N subframesand wherein the signalling information comprises N bits, correspondingto one bit for identifying if a corresponding one of the N subframescarries the common control data for reception and decoding by the MTCuser devices.
 12. A communications node according to claim 6, whereinthe communications node is configured to communicate with the userdevices using radio frames having N subframes and wherein the signallinginformation comprises M bits, where M is less than N, that identify oneof a number of predetermined configuration of the N subframes that willcarry the common control data for reception and decoding by the MTC userdevices.
 13. A communications node according to claim 12, wherein thedata identifying the subframes identifies multimedia broadcast singlefrequency network, MBSFN, subframes and non-MBSFN subframes as carryingthe common control data for reception and decoding by the MTC userdevices and wherein the M bits jointly encode which MBSFN subframes andwhich non-MBSFN subframes of a radio frame will carry the common controldata for reception and decoding by the MTC user devices.
 14. Acommunications node according to claim 5, wherein the communicationsnode is configured to transmit the common control data for reception anddecoding by the MTC user devices in subframes that do not includechannel state information reference signals, CSI-RS, or channelreference signals, CRS.
 15. A communications node according to claim 5,wherein the communications node is configured to transmit the commoncontrol data for reception and decoding by the MTC user devices insubframes that include channel state information reference signals,CSI-RS, or channel reference signals, CRS; and is configured to avoidusing resources to carry the common control data for reception anddecoding by the MTC user devices that are used to carry the CSI-RS orthe CRS.
 16. A communications node according to claim 1, wherein thecommunications node is configured to transmit signalling information tothe MTC user devices identifying the location within a subframe of thecommon control data for reception and decoding by the MTC user devices.17. A communications node according to claim 16, wherein there is afixed number of possible locations within a subframe for the commoncontrol data for reception and decoding by the MTC user devices, andwherein the communications node is configured to signal data identifyingone of the possible locations.
 18. A user device for communicating witha communications node, characterised in that the user device isconfigured to operate with the communications node of claim 1 andadapted to be able to receive and decode the common control data tocontrol communications with the communications node.
 19. A methodperformed by a communications node that schedules resources for use by aplurality of user devices, including legacy user devices and MachineType Communications, MTC user devices, for communicating with thecommunications node, the method comprising: generating control data fortransmission to the user devices, the control data including commoncontrol data for reception and decoding by a plurality of user devicesand user specific control data for reception and decoding by a specificuser device; transmitting the generated control data in a sequence ofsubframes for reception by the user devices; generating common controldata for reception and decoding by the MTC user devices; andtransmitting the common control data for the legacy user devices on afirst channel and the common control data for the MTC user devices on asecond channel which is not monitored by the legacy user devices; andwherein the transmitting transmits repeats of the common control datagenerated for reception and decoding by the MTC user devices within aplurality of subframes.
 20. A user device for communicating with acommunications node, the user device comprising: a transceiver circuitconfigured to receive control data transmitted by the communicationsnode, the control data including common control data for reception anddecoding by the user device and user specific control data for receptionand decoding by a specific user device; wherein the received commoncontrol data is for reception and decoding by Machine TypeCommunications, MTC user devices; wherein the transceiver circuit isfurther configured to receive the common control data on a channel whichis not monitored by the legacy user devices; wherein the transceivercircuit is further configured to receive a plurality of subframescomprising said common control data; a controller configured to combinethe control data received from the plurality of subframes; and whereinthe controller is further configured to decode the combined commoncontrol data.